Now I happen to enjoy the goofy writing alot. Most of the dialogue felt in character for sure, except the starting dialogue (stuff about neets and all this just feels like a fandom insert joke) It was fun seeing the two bounce off each other and it gave me more investment into the game.
This is one thing you should most certainly take forward with regarding this game if you ever expand upon it in future.
Gameplay wise, not gonna lie, it was rough. The concept is interesting, sure, but it was incredibly buggy and inconsistent. The platforming bugged out regarding gravity many many times (Gravity kept it's velocity as you turned, and you'd sometimes instantly accelerate right into a pit, as well as the platforms which were incredibly hard to consistently activate.
And Mokou being the only one to attack felt like a wasted opportunity. I would of liked if say, Kaguya could slow enemies down. Would of been cool. Same with Mokou not really being used to say, set stuff on fire for a puzzle. Could of been cool.
I did like the gravity mechanic on a conceptual level, as well as switching between Mokou and Kaguya on the fly being needed. It's just the idea needed more fleshing out.
Visuals, I enjoyed how you depicted both their characters in extremely stylized ways. It made it entertaining to see and I would like to see other characters interpreted one day as well. Because it's a fun art style
The backgrounds are average though. Maybe make them pick up to the same standard of exaggeration and style as the characters if you every come back to this idea.
Music's alright.
Overall, I enjoyed it. Mostly for the writing and the concept, but regardless it was fun. I say grab the idea and refine it, I'd like to see what happens if you make a small but polished game out of this. Because this game was damn endearing.
I wish you luck in future.
(Also I was apart of the Game jam too with DanmakuDragon, if you want to give your own feedback you're totally welcome to :D https://itch.io/jam/touhou-jam-6/rate/912501)